The invention relates to a method for controlling the supply of a pressure medium on rail vehicles, as well as to a respective device.
The applicant""s German Patent Document DE 198 48 995 A1 reveals a main air reservoir pipe which, conforming to standards, extends through all rail vehicles of a train formation and can be connected at the coupling points. This common pressure medium pipe is connected to the main air reservoirs, one on each rail vehicle. The main air reservoirs store the pressure medium in the form of compressed air which is required for the operation of braking devices as well as other pressure-medium-operated aggregatesxe2x80x94such as door opening systems. In addition to the main air reservoir pipe, a second so-called main air pipe usually also extends through the train formation. However, this main air pipe fed by way of a train brake valve is used only for controlling the braking devices of the train formation, that is, for transmitting the braking signal. To this extent, the aggregates controlled by the main air pipe do not significantly contribute to the pressure medium consumption within the train formation.
For feeding the system of the main air reservoir pipe with respect to the pressure medium demand, compressors are customarily used. In a known manner, a compressor subjects air taken in from the atmosphere, by means of a mechanical driving energy, by compression to an excess pressure. The compressors, which are present in a decentralized manner on each individual rail vehicle of the train formation, are mutually connected with respect to the pressure medium by means of the common main air reservoir pipe.
The control of this pressure medium supply within the train formation can take place in a generally known manner by an independent decentralized pressure control. By means of a local pressure sensor assigned to each local compressor, the condition of a pressure medium requirement within the train formation can be determined. A pressure medium demand arises when the pressure in the main air reservoir pipe falls below a defined limit pressure. In this case, a switching device, connected on the input side with the local pressure sensor, switches on the local compressor in order to cover the pressure medium demand. The switching device will then switch the compressor off again when the reaching of an also defined maximal pressure is indicated by the pressure sensor. This so-called pressure monitor is thereby based on the principle of an on-off control.
The significant disadvantage of the known decentralized on-off control is the uncoordinated interaction of the compressors within the train formation. Although, as a result of the decentralization, a self-sufficient pressure medium supply is achieved for each rail vehicle which most easily allows a freely selectable mutual coupling of the rail vehicles, the resulting uncoordinated interaction leads to an increased wear of the compressors, which causes high expenditures with respect to maintenance and a shortened service life of the compressors. Thus, for example, tolerance differences in the pressure sensors in the reference system of the train formation may have the effect that always only a single compressor is used for meeting a low pressure medium demand occurring during the operation, whose assigned pressure monitor triggers at a limit pressure value which is still in the tolerance range but is minimal. During its entire service life, this compressor will then be stressed comparatively more frequently than the other compressors. This one-sided stressing of a compressor increases its wear, so that it also has to be serviced at shorter intervals.
On the other hand, in the event of a greater pressure drop below the limit value, all compressors are immediately switched on jointly in order to cover the arisen pressure medium demand. However, in most cases, an operation of all compressors is not necessary because even a few compressors can cause a maximal pressure within a very short time. The starting phase of all compressors in the case of a joint switch-on results in a high energy consumption as well as in unnecessary peak loads in the energy system of the train formation.
From European Patent Document EP 0 829 405 A2, a corresponding method as well as a corresponding device are known for controlling the pressure medium supply in the case of rail vehicles. Here, a synchronous admission of pressure medium to pressure pipe, which all compressors have in common, takes place by control valves which are controlled from a data bus.
From German Patent Document DE 198 37 100 A1, a system is known for controlling compressors of a train formation, in the case of which several compressors of a different capacity are provided which, corresponding to their capacity are actuated successively or individually, so that each respectively activated compressor operates at an optimal utilization ratio of the operating period to the rest period. A disadvantage of this solution consists of the fact that, for the refilling of a slight pressure difference, usually only the compressor with the lowest capacity is used, whereas the compressors with the higher capacities are less frequently actuated. This results in an enormous disproportion when used within a train formation.
It is therefore an object of the present invention to further improve the control of the pressure medium supply in the case of rail vehicles such that a utilization of the compressors existing in the train formation is achieved which is as balanced as possible in order to minimize particularly the wear and the energy consumption of the compressors.
The method of the invention includes, corresponding to the total number of compressors available in the train formation, a fixed or alternating priority sequence is defined for the compressors. Depending on the actual pressure medium demand, only that number of compressors will be caused to operate according to the sequence of their priority which are required for covering the actual pressure medium demand.
The advantage of the control method according to the invention for the compressors of the train formation is the demand-based on-and-off switching of the required compressors which is carried out as a function of the priority according to a fixed sequence which, however, is optionally freely changeable. A change of the priority sequence can take place under certain triggering conditions which will be explained in greater detail below. Since all compressors no longer contribute to the pressure medium supply in an equal manner, the on- and off-switching frequency can be significantly lowered, which minimizes wear and saves energy. In order to service, for example, a constant pressure medium consumption, the compressors with the highest priority run predominantly constantly at their optimal operating temperature, at which the wear is low. A low additional pressure compensation at operationally caused pressure fluctuations can then be carried out by the compressor with the next highest priority, which, however, is connected only as required.
For such a compensation of operationally caused pressure fluctuations in the main air reservoir pipe, in the event of a pressure drop below a defined low limit values, in addition to the already switched-on compressors, preferably first the compressor with the next higher priority is caused to operate. When a maximal pressure is reached, analogously, first the compressor with the next lower priority of the switched-on compressors is then caused to cease its operation. This control concept by means of two pressure limit values therefore follows the principle of the on-off control.
According to another measure improving the invention, when the operation of the pressure medium supply of the train formation is started, the compressors are switched on at different time delays. When the maximal pressure is reached, these are then switched off again at different time delays, the switching-on and off respectively taking place after the expiration of a time period defined as a function of the priority of each compressor. The time-related switch-on delay prevents a disadvantageous power peak in the energy consumption so that a dependable standing start of the compressors can take placexe2x80x94for example, when the pressure medium supply is actuated after an assembling of the train formation from individual rail vehicles.
For defining the priority sequence of the compressors, the compressors are preferably switched on at different individual lower limit pressures and are switched off again at different individual upper limit pressures. In this case, essentially the compressor with the highest priority is switched on first because of the largest lower limit pressure for a refill and, because of the largest upper limit pressure is switched off again last. The compressors which follow with respect to the priority being switched on and off respectively by, in each case, a next differential pressure value in an offset manner. In a simple fashion, this pressure staggering results in the priority sequence according to the invention for the compressors and permits a successive load-optimal approximation to the maximal pressure of the pressure medium supply. In addition, it is also conceivable to define the priority sequence of the compressors differentlyxe2x80x94for example, by a higher-ranking electronic control unit. In this case, the electronic control unit can be connected with the switching devices of all compressors for the controlling by a data bus extending through the train formation. The controlling of the pressure medium supply within the train formation can therefore take place in a centralized manner from a higher-ranking electronic control unit or in a decentralized manner by a control unit assigned to each compressor, in the latter case, a mutually coordinated adjustment being required. In the simplest case, the control unit may be constructed as a conventional pressure monitor on the compressor, which pressure monitor can be adjusted for setting its priority. By way of a common data bus, an advantageous master/slave assignment and therefore a centralization of the control can be achieved. In the simplest case, an electrical or mechanical manual selection switch or the like constructed directly on the compressor is suitable as the device for the decentralized defining of a priority sequence.
The priority sequence of the compressors may remain defined in an unchanged manner after the assembling of the rail vehicles to a train formation. However, a changeability of the priority sequence is particularly advantageous. Such a repriorization may take place in a fixedly or randomly time-controlled or pressure-controlled, temperature-controlled or moisture-controlled manner or in any other suitable manner. The change in the priority sequence of the compressors has the advantage of a uniform scattering of the wear and thus a particularly balanced utilization of all available compressors. Extremely varying maintenance intervals for compressor systems of the rail vehicles can thereby be avoided. The change of the priority sequence therefore provides a uniform rotation in the utilization frequency of the compressors in the train formation. Since, as a result, an extended stoppage of each compressor and therefore an absolute cooling is avoided, a wear-causing moisture release of compressors, which occurs in the warm-up phase, can be effectively prevented.
For a time-controlled change of the priority sequence during the operation of the pressure medium supply, preferably when a defined uninterrupted operating period is reached, the compressor with the highest priority is changed to the lowest priority and is therefore switched off. This compressor is replaced by a compressor with the next higher priority. In addition, other time-controlled changing methods are also conceivable. Thus, a change of the priority sequence can also be coupled to a fixed hour or date change as a triggering event.
In the case of an alternative pressure-controlled change of the priority sequence during the operation of the pressure medium supply, when a defined switch-over pressure value is reached within the main air reservoir pipe, the compressor with the highest priority can be changed to the lowest priority and can thereby be switched off. This compressor is again replaced by a still switched-off compressor with the next higher priority. In the simplest case, the switch-over pressure value triggering a change in the priority sequence, for example, after a significant pressure drop, can be caused by a braking of the train formation to a stoppage.
For an also conceivable temperature-controlled change of the priority sequence during the operation of the pressure medium supply, when the operating temperature is reached and after the expiration of a defined holding time, the compressor with the highest priority can be changed to the lowest priority and can therefore be switched off. This compressor, in turn, being replaced by a still switched-off compressor with the next higher priority. The temperature-controlled change therefore represents a measure aimed at the optimization of an operating mode of the compressors which is as dry as possible.
For an alternative moisture-controlled change of the priority sequence, during the operation of the pressure medium supply, the compressor with the highest priority is changed to the lowest priority when a dry operating condition is reached and is therefore switched off. This compressor being replaced by a still switched-off moist compressor with the next higher priority. This moisture-dependent control, which can be achieved by suitable sensors, therefore represents another conceivable possibility with a view to the optimization of an operating mode of the compressors which is as dry as possible.
In addition, other control methods for changing the priority sequence are also conceivable which relate to suitable parameters in the pressure medium supply, from which causes of wear can be derived. A mutual combination of several control methods is also conceivable.
These and other aspects of the present invention will become apparent from the following detailed description of the invention, when considered in conjunction with accompanying drawings.